Prior art techniques for obtaining fingerprints have included application of ink to a person's fingertips and rolling or simply pressing the tips of the individual's fingers to appropriate places on a recording card. This system has severe limitations, the least of which is the use of ink which can often require several attempts before a usable image is obtained. Furthermore, use of an ink-based system requires cooperation of the individual from whom the prints are being taken, since blurring and smearing of the prints often occurs when attempts are made to obtain fingerprints from a hostile individual. Additionally, it is difficult to easily adapt inked prints for computerized storage and retrieval; thus making it difficult for various governmental agencies to reliably transfer and share data.
Several attempts have been made to optically acquire fingerprint images, however known systems have various drawbacks. In order to record data correctly, it is necessary to utilize trained personnel to aid the individual in guiding his/her fingers over the optical reading area. The fingers must be accurately positioned and the rate of rotation of the fingers must not exceed the recording abilities of the device. If the fingers are not rotated at the correct speed, data will be lost necessitating repeating of the entire procedure.
Several of these systems generate an optical image in real time, but they suffer from errors caused by their need to approximate the complete fingerprint image by electronically combining a plurality of smaller images or "slices" and smoothing the edges of the slices together to form an image which has the appearance of a full fingerprint. In performing the smoothing operation, a composite image is created which averages the data contained in the adjacent image slices, discarding discontinuities and artifacts so as to arrive at what can be described as a "best guess" image.
Improvements on this so-called "best guess" scenario have sought to provide overlapping slices wherein the image is formed by generating a composite array as a mathematical function of a comparison and an average of the overlapping data which constitutes the overlapping portions of adjacent slices. While this method more accurately characterizes transitions between the boundaries of adjacent image slices, the averaging of discontinuities and discarding of artifacts continues to prevent the obtention of images having the desired degree of accuracy and resolution. Such images still engender a degree of inaccuracy which, when coupled with the limits of resolution and recording inherent in the available hardware, render them unacceptable.
U.S. Pat. No. 4,933,976 discloses a method for generating data characteristic of a rolled fingerprint image. The method requires storing arrays of digital data characteristic of adjacent and overlapping fingerprint images of portions of the finger as the finger is rolled across an optical device, the optical device capturing the image and generating a composite array of digital data characteristic of a rolled fingerprint image as a mathematical function of overlapping image portions of the fingerprint.
What is lacking in the art is a method and apparatus for reliably recording accurate high resolution electronic optical images of fingerprints without the necessity of adhering to critical sampling procedures. Such an invention would enable an untrained individual to accurately record fingerprint images which do not inherently contain unacceptable errors due to averaging of the image while processing.